Effect of ultrasonic vibration on TIG welding–brazing joining of aluminum alloy to steel

Ultrasonic vibration (USV) can optimize the microstructure of the seam and enhance the mechanical properties of the joint; thus, it has been employed to profitably assist Al/steel welding–brazing. The effects of USV on Al/steel welding–brazing joining were investigated. Without the USV treatment, coarse aluminum dendrites, the second phases of Al–Si eutectic and Al3FeSi with large sizes were formed in the joint. Under the USV treatment, the refinement of the aluminum matrix, spheroidization of the Al–Si eutectic, and fragmentation of Al3FeSi were produced, which resulted from the effects of cavitation and acoustic streaming induced by the USV treatment. The maximum value of the tensile shear strength of the ultrasonic–treated joint could be achieved at an optimum ultrasonic vibration power of 0.8 kW, which had ∼30% increment compared with the raw joint, owing to the fine–grained strengthening and dispersing strengthening of Al–Si eutectic and Al3FeSi. The ductile fracture was located in aluminum base metal.